In a hydraulic brake booster, a valve assembly is provided for controlling the communication of pressurized fluid between an accumulator and a pressure chamber. than in the pressure chamber and Pressurized fluid is communicated from the accumulator to the pressure chamber in response to an actuator which is engageable with the valve assembly when the level of fluid pressure in the pressure chamber is inadequate to provide a power assist during braking.
If the level of pressurized fluid within the accumulator should reach an excessive level, due to heat and improper venting, the accumulator is deformable to vent a storage chamber to an engine compartment wherein a fire hazard may be created when the pressurized fluid coming in contact with a hot exhaust system.